Process of tanning hides with polymethoxyaldehyde compounds and optionally vegetable tanning



United States Patent r PROCESS OF TANNING HIDES WITH POLYMETH-OXYALDEHYDE COMPOUNDS .AND "OPTION- ALLY VEGETABLE TANNING Martin L.Fein, Riverside, N.'J.,-and Edward M. Filachione, Philadelphia, Pa.,assignorsto-the United Statesof America as represented by the SecretaryofAgriculture No Drawing. Application January 3, "1956 'Serial No.557,217

3 Claims. (Cl. 8-94.21

(Granted under Title 35, U. S. Code (1952), sec. 266) A non-exclusive,"irrevocable, royalty-free license in the invention herein described,throughout the world for all purposes of the United States Government,with power to grant sublic'enses forsuch purposes, is'hereby granted tothe Government of the United States of America.

This invention relates to new reagents and newproces'sesfortanning'hide's.

From time immemorial, man has largely depended on natural vegetabletannins for converting animal hides into leather. However, the supply ofsuch materials is constantly diminishing and "their cost increasing;consequently, great efforts have been made to develop suitable syntheticmaterials to replace the vegetable tannins. While many such syntheticshave been used or suggested, none has been entirely satisfactory, eitherbecause of high cost or deficiencies in the properties of the leatherproduced thereby.

Accordingly, it is an object of this invention to provide new synthetictanning agents that may be economically manufactured in any requiredamount and that react rapidly with hide substance to give a satisfactorytannage.

The process of the invention utilizes as tanning agents a class oflong-chain aliphatic aldehydes called generically polymethoxyaldehydesand having the structure wherein n has an average value of 2 to 20. Suchaldehydes are readily obtainable by the hydrolysis of the correspondingacetals, particularly the methyl acetals having the formula O OH: OCH:

These acetals may be obtained by the condensation of methyl vinyl etherand methanol by any known process, such as, for instance, thosedescribed in US. Patents 2,165,962 and 2,487,525. Because of the greatreactivity and consequent instability of the free aldehydes, wegenerally prefer to store them in the form of the acetal. The freealdehyde is then generated just prior to its use or it may actually begenerated in situ during the tanning process.

Since the polymethoxyaldehydes are polymeric in na- I 2,880,053 PatentedMar. 31, 1959 "the individual molecules of which wvillhave diflerentchain lengths and valuesof n. I

-In the interest of brevity and simphcity, 'the average value of n inparticular lots of material will be des1gnated hereinafterfby theappropriate ,numeralsufiix; thus,

polymethoxyaldehyde i .re'fers ton material in which the average valueof 'n is :4. flhiswe-abbreviate as PMA-4.

By the term hides": as used herein xwezmean any animal skin that is:commonly tanned, such as cowhide, horsehide, ca-lfskin, pigskin,sheepskin sand .goatskin, .as well as :any such hide that has :alreadybeen partially or completely tanned by a-conventional tanning process.Any hide, as :so defined, :can .be tanned by treatment with apolymethoxyaldehyde as shown hereinafter.

According to the invention, :liides are tanned :by immersion for :asuitable time fin a solution of polymethoxyaldehyde .in water or a:suitable organic .solvent. No

special preparation of the hide is necessary, the usual preparation forconventional Etannage being entirely 'sat- I isfactory. Likewise the:amount and concentration of tanning solution may be varied widelywithout detrimental aeifect. The affinity of the polymethoxyalde'hydesfor the hide substance :is such :that dilute solutions are substantiallyexhausted by the hides, yet the use of a large excess of tanning agentresults in no loss because the hide, when fully tanned, ceases to absorbthe aldehyde.

The practice of the invention is illustrated by the following examples.

Preparation of polymethoxyaldehydes.-Polymethoxyacetals having averagevalues of n in the above formulas of 4, 9 and 14 were hydrolyzed to thealdehyde by stirring at room temperature with several times their volumeof 1% aqueous hydrochloric acid until substantially all the acetaldissolved in the water layer. The small amountof insoluble materialcould be brought into solution' by addition of a little alcohol oracetone, left in suspension or mechanically separated. Theaqueoussolution of aldehyde was adjusted to they desired pH by additionof alkaline reagents and/or buffers. If desired, the aldehyde may besimilarly prepared in a suitable organic solvent such as a loweraliphatic alcohol or ketone.

Tanning with polymethoxyaldehydes.-The aldehyde solutions prepared asdescribed above were adjusted to the desired concentration, usually inthe range 5 to 25%, though higher or lower concentrations could be usedwithout difliculty; the pH was adjusted by use of suitable bufiers;salts such as sodium chloride or sulfate were added if desired and thehide, previously adjusted to the isoelectric point, was immersed in thesolution. After being left at room temperature for various times, withcontinuous agitation, samples of the hide were cut out, tested forshrink temperature (Ts) and examined for leatherlike properties.Although the elevation in Ts was only moderately high, the samples,after being washed and dried were light colored and showed excellentleatherlike properties. A summary of the results of some typicalexperiments is shown in Table I.

Table L-Tafining with polymethoxyaldehydes (PMA) Treatment ShrinkageTemp., C., after- Example Aldehyde Butler Salt pH 1 day 2 days 3 days 6days Cowhide:

1 PMA-4.-- Lactic acld,5 NaCl, 5% 3.3 60 6O 60 60 NSHCO), 0.2 None.--7.1-7.0 74 77 77 70 7.1-7.5 74 77 77 11. 1-10. 9 73 74 74 g0, 1 NaCl, 3a 10.6-10.4 72 75 77 7s Lactic acid, NaCl, 5% 3. 6-3.7 63 61 70 NaHCQ;,0.2M-.- None 7.3-7.7 70 72 72 74 NaHCOfi 0.2M.-. NaCl,4% 7.1-7.4 68 7072 g 1 0' N801, 3 10.2-10.1 68 e9 72 73 Lactic acid, 5%..- NaCl, 4', 3.6-3. 7 60 60 60 NaHCO;, 0.2M.-. None 7.3-7.7 70 73 73 74 NaHCO;,0.2M---NaCl,4 o 7. 2-7.6 68 70 71 J MgO, 1% NaCl,3 10.5-10.3 67 68 72 72Lactic acid, 5% 3. 3 58 60 61 -NaHCO;, 0.2M.-- None 7.3-7.0 73 74 74 74MgO, 0.47 10. 5-10. 7 69 71 SE00; 7. 3-8. 0 68 70 73 NaHGO; B. 0-8. 3 01e9 71 73 1 Results similar to those shown in the table were ob- Weclaim: tained when other kinds of hide, such as horsehide, pig- 1. Theprocess for tanning hides comprising impregskin, sheepskin, goatskin orfur skins were used, or when mating the hides with an alkaline solutionof a polymeththe PMA was dissolved in alcohol, acetone or similaroxyaldehyde having the formula organic solvent instead of water.Likewise, PMA of OH:(CHCH,)..CHO h1gher or lower molecular weights, 1nthe range of PMA-2 CH 1 to PMA-20 gave equally satisfactory results.There is some advantage in using the lower molecular weight where! hasan average value 2 to 20 the 111d materials, such as PMA-2 to 10, inthat they are more are tannedefiective, pound for pound, they penetratethe hide faster The P of dam! wherein the hlde 15 51's! and they areeasier to prepare fmm the acetaL tanned with vegetablev tannin andsubsequently tanned Combination vegetable-aldehyde tannage in which Wlthapolymethoxyaldeilyde- 1 vegetable tanned leather was retanned with PMAor in The Process of 51mm 1 whereln the hide, after b61118 which PMAtanned leather was .rctanned with vegetable tannins gave productssuperior to those obtained by either tannage alone. They had highershrink temperatures, were fuller and firmer and had better appearance.Furthermore retannage of the PMA tanned leather with vegetable tanninsresulted in a much-more rapid penetration by the latter agent.

tanned with a polymethoxyaldehyde, is subsequently tanned with vegetabletannin.

References Cited in the file of this patent UNITED STATES PATENTS

1. THE PROCESS FOR TANNING HIDES COMPRISING IMPREGNATING THE HIDES WITHAN ALKALINE SOLUTION OF A POLYMETHOXYALDEHYDE HAVING THE FORMULA
 2. THEPROCESS OF CLAIM 1 WHEREIN THE HIDE IS FIRST TANNED WITH VEGETABLETANNIN AND SUBSEQUENTLY TANNED WITH A POLYMETHOXYALDEHYDE.